Rules on products sold in the west. Most manufacturing companies already need to trace the origin of their components, so you could specify what products are and aren't allowed to be sold in the west.
And how would that help the working conditions in China?
You’d just shift the manufacturing to a less hostile environment, where the government doesn’t intentionally make it hard to do auditing on modern slavery. Like India.
I just don’t see how it would help the Chinese labour situation at all.
If china wants to deliver to the west they'll need to improve working conditions. Chinese companies will deliver at spec for lowest cost, if you up the spec, they'll adjust and increase cost adjustingly.